Modern high-speed airborne mobile platforms, for example jet aircraft, must meet performance requirements which call for an air induction system of substantial complexity. The inlet must provide intake air to the engine at a quantity and quality necessary to meet thrust requirements throughout the aircraft flight envelope. Accordingly, it must have a configuration which can efficiently receive and compress intake air at a variety of speeds and altitudes. Further, the inlet should have a compact volume so that it fits within tightly limited space constraints. The configuration of the inlet should facilitate uniformity in the flow of intake air and minimize adverse impacts to the aircraft. That is particularly difficult in an aircraft which has a complex aerodynamic shape. For example, some aircraft have edges and/or surfaces which are angled in two directions (i.e., swept back with respect to both the vertical and horizontal planes). Ideally, the inlet should conform to that contour and minimize generation of secondary flows and shock waves which produce flow non-uniformities.
Unfortunately, previous inlets fail to fully meet these needs. For example, some inlets have required a length for accomplishing compression of intake air which is excessive for the space available in the aircraft configuration. That necessitates a substantial re-design effort or, alternatively, a degradation of performance. Other inlets have configurations which sharply limit the potential location or size relative to the surrounding aircraft fuselage.
Another constraint on certain aircraft which operate at supersonic speed is the need to “start” the inlet. As known to those skilled in the art, an inlet having internal compression or mixed compression is designed to compress intake air moving at a supersonic speed within the interior of the inlet duct. The inlet must initially “swallow” a structure of shock waves when exceeding its starting Mach number in order to establish a stable condition where the inlet operates as intended. When the inlet is “unstarted,” a phenomenon in which all shock waves remain outside of the inlet, the thrust produced by the engine is reduced substantially. A process for starting the inlet has typically required a variable geometry duct which provides a capability to increase flow passage size and receive a larger quantity of intake air, thereby swallowing the shock waves. Unfortunately, that capability requires additional complexity and weight.